A 29Si MAS NMR study of tetrahedral site distributions in the layered silicic acid H+-magadiite (H2Si14O29 · nH2O) and in Na+-magadiite (Na2Si14O29 · nH2O)

Hypothetical Structures of Magadiite and Sodium Octosilicate and Structural Relationships Between the Layered Alkali Metal Silicates and the Mordenite- and Pentasil-Group Zeolites

“…The Qa/Q3 ratio for magadiite heated to 2500C is given as large in Table 3 could not be quantified precisely. Thus, the differences between the Q4/Q3 ratios in Table 3 and those reported for magadiite by Schwieger et al (1985) and Pinnavaia et al (1986) are probably due to cross-linking of silanol groups from adjacent layers forming siloxane linkages and resulting in more condensed structures having a higher Q4/Q3 ratio. The increase in the Q4/Q3 ratio of magadiite on heating to 250~ ( Figure 6, Table 3), also observed by Pinnavaia et al (1986), suggests that the layer silicate structure condensed on heating to a material which became enriched in Q4 domains at the Garcrs, Rocke, Crowder, and Hasha and -111 ppm are present in the Q3 and Q4 regions, suggesting a structure having a significant degree of condensation.…”

“…These structures contain sheets of 6-member rings of HOSiO 3 or MOSiO 3 tetrahedra (Q3 type), in which three of the four oxygens are bonded to adjacent silicon atoms and the fourth is bonded to a H atom or to an alkali metal atom, M. The sheets of tetrahedra are similar to those in mordenite-group structures, but they are not linked to each other to form three-dimensional frameworks. Schwieger et al (1985) and Pinnavaia et al (1986) recently proposed structures for several layered alkali metal silicates that contain both Q3 and Q4 tetrahedra. In the Q4 tetrahedra, the four oxygen atoms bridge adjacent silicon atoms.…”

Thermoanalytische Untersuchungen an aluminiumfreien Schichtsilikaten

“…Die Struktur dieser Schichtsilikate ist nicht aufgekl~irt. Auf Basis von NMR-und Pulverdiffraktionsuntersuchungen sowie den bekannten chemischen Zusammensetzungen wurden Modellvorstellungen fiir den Aufbau der "Bulk"-Schichten entwickelt, die insbesondere das chemische Reaktionsverhalten dieset Materialien hinreichend erklaren k6nnen [12][13][14][15]. Abbildung 1 zeigt schematisch den Aufbau eines Schichtsilikates vom Metallsilikathydrattyp (a), die Modellvorstellung ffir eine Magadiit-Bulkschicht (b) und das typische RSntgendiffraktogramm des Magadiits (c) [12,16].…”

Characterization of Silanol Groups in Protonated Magadiite by 1H and 2H Solid-State Nuclear Magnetic Resonance

“…Because magadiite has poor crystallinity and large single crystals are not available (Brindley, 1969), its structure has not been refined. Although many structural models have been proposed on the basis of the chemical composition, infrared (IR) analysis, and the ratio of Q3 [HOSi(OSi)3] to Q4 [Si(OSi)4] environments obtained by 29Si magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) (Almond et al, 1996(Almond et al, , 1997Brandt et al, 1987Brandt et al, , 1988Garc6s et al, 1988;Huang et al, 1999;Pinnavaia et aL, 1986;Scholzen et al, 1991;Schwieger et al, 1985), the structure of magadiite is still obscure. On the other hand, intercalation reactions and further silylation reactions involving magadiite (Mercier et aL, 1994;Ogawa et al, 1998a;Okutomo et al, 1999;Ruiz-Hitzky and Rojo, 1980;Ruiz-Hitzky et al, 1985;Yanagisawa et al, 1990Yanagisawa et al, , 1988aYanagisawa et al, , 1988b) have attracted considerable attention for many applications, such as in adsorbents (Hadjar et al, 1995;Ogawa et al, 1998b) and microporous materials (Dailey and Pinnavaia, 1992;Landis et al, 1991;Sprung et al, 1990;Wong and Cheng, 1993;Yanagisawa et al, 1991).…”